1. Field of the Invention
The present invention relates to a cap with valve, such as a fuel cap or a radiator cap for automobiles, which is installed to an aperture of a container such as a fuel tank or a radiator and adjusts pressure in the container by flowing fluid such as air out of the container or into the container from outside when the pressure in the container is positive or negative.
2. Description of the Prior Art
In the prior art, such cap with valve, for example, a fuel cap to be installed to a filler neck of automobiles (hereinafter referred to simply as "cap"), depending on difference of shape of a lip element in the valve body, the valves are classified into two sorts as shown in FIG. 1 and FIG. 2 (refer to Japanese patent publication No. 52-45924, Utility model publication No. 58-47002, Utility model application laid-open No. 60-179654).
In an annular valve body 3 in a cap 1 shown in FIG. 1, its inner circumferential lip element 3a and outer circumferential lip element 3b are projected in reverse directions to each other. Also in an annular valve body 13 in a cap 11 shown in FIG.2, its inner circumferential lip element 13a and outer circumferential lip element 13b in the same direction.
In the cap 1, at normal state, the outer circumferential lip element 3b together with a first annular support plate 4 is biased downward by a first coil spring 6 and pressed against an annular projection 2b of a cap body 2. Also the inner circumferential lip element 3a together with a second annular support plate 5 is biased upward by a second coil spring 7 and pressed against a bottom portion 8b of a spring shoe plate 8. That is, these lip elements 3a, 3b are pressed at prescribed position so as to close a fluid flow path 2a of the cap body 2. When pressure in the fuel tank becomes positive pressure over prescribed valve, the outer circumferential lip element 3b is bent about a thin portion 3c of the valve body 3 as fulcrum and elevated together with the first support plate 4 against the biasing force of the first coil spring 6 and separated from the annular projection 2b of the cap body 2. Thus the positive pressure state in the fuel tank is eliminated through a gap between the outer circumferential lip element 3b and the annular projection 2b. Also when the pressure in the fuel tank becomes negative pressure over prescribed value, the inner circumferential lip element 3a is bent about the thin portion 3c as fulcrum and lowered together with the second support plate 5 against the biasing force of the second coil spring 7 and separated from the bottom portion 8b of the spring shoe plate 8. Thus the negative pressure state in the fuel tank is eliminated through a gap between the inner circumferential lip element 3a and the bottom portion 8b of the spring shoe plate 8.
Also in the cap 11, at normal state, the outer lip element 13b together with an annular support plate 14 is biased downward by a first coil spring 16 and pressed against an annular projection 12b of a cap body 12. Also the inner circumferential lip element 13a pressed against a disk shaped valve plate 18 biased upward by a second coil spring 17. That is, these lip elements 13a, 13b are pressed at prescribed position so as to close a fluid flow path 12a of the cap body 12. When pressure in the fuel tank becomes positive pressure over prescribed value, the outer circumferential lip element 13b together with the support plate 14 is elevated against the biasing force of the first coil spring 16 and separated from the annular projection 12b of the cap body 12. Thus the positive pressure state in the fuel tank is eliminated through a gap between the outer circumferntial lip element 13b and the annular projection 12b. Also when the pressure in the fuel tank becomes negative pressure over prescribed value, the valve plate 18 is lowerd against the biasing forece of the second coil spring 17 and separated from the innter circumferential lip element 13a. Thus the negative pressure state in the fuel tank is eliminated through a gap between the inner circumferential lip element 13a and the valve plate 18. Numeral 10 designates a filler neck.
In such caps 1, 11 in the prior art, seal surface pressure of the lip elements 3a, 3b, 13a, 13b is an important factor to determine good valve characteristics (seal characteristics, valve opening characteristics) of the valve bodies 3, 13. The higher the seal surface pressure gives the better the seal characteristics. The seal surface pressure becomes ##EQU1## When the shape of the valve body, i.e., diameter of the lip element or the contact width of the lip element with the seal portion, is the same, the seal surface pressure becomes higher as the biasing force of the spring becomes larger.
In such valve body, however, the valve opening must be performed at prescribed pressure. The biasing force of the spring has relation that spring biasing force (kg)=valve opening pressure (kg/cm.sup.2).times.pressure receiving area (cm.sup.2).
Consequently, the above-mentioned formula becomes ##EQU2##
The narrower the seal portion contact width of the lip element, the better the seal characteristics. However, the seal characteristics are limited by the durability and therefore becomes nearly constant in each seal member. Consequently, in the valve body where the diameter of the lip element and the valve opening pressure are set to contact valve, the valve body having the pressure receiving area can obtain the high seal surface pressure and prescribed valve opening characteristics so that good valve characteristics can be easily obtained.
Under consideration of the pressure receiving area, the caps 1, 11, will be studied where the valve bodies 3, 13, comprising the inner circumferential lip elements 3a, 13a, having the same diameter d and the outer circumferential lip elements 3b, 13b having the same diameter D are used, and the valve opening pressure is the same at the positive pressure state and the negative pressure state.
The pressure receiving area of the inner circumferential lip elements 3a, 13a will be studied.
The pressure receiving area X1 of the inner circumferential lip element 3a in the cap 1 becomes the annular area between the inner circumferential lip element 3a and the thin portion 3c since the inner circumferential lip element 3a is bent about the thin portion 3c as fulcrum. If the diameter of the thin portion 3c is made A, it follows that EQU X1=(A.sup.2 -d.sup.2).pi./4
Since the pressure receiving area X2 of the inner circumferential lip element 13a in the cap 11 becomes the area surrounded by the inner circumferential lip element 13a, it follows that EQU X2=d.sup.2 .multidot..pi./4
Comparing both pressure receiving areas X1, X2, if the diameter d is sufficiently small and less than 1/.sqroot.2 times of the diameter A, the pressure receiving area of the valve body 3 of the cap 1 becomes larger and therefore the cap 1 type can easily obtain good valve caracteristics at the negative pressure state.
Next, the pressure receiving area of the outer circumferential lip elements 3b, 13b will be studied.
Since the outer circumferential lip element 3b is bent about the thin portion 3c as fulcrum, the pressure receiving area Y1 of the outer circumferential lip element 3b in the cap 1 becomes the annular area between the outer circumferential lip element 3b and the thin portion 3c. That is EQU Y1=(D.sup.2 -A.sup.2).pi./4
The pressure receiving area Y2 of the outer circumferential lip element 13b in the cap 11 becomes the area surrounded by the outer circumferential lip element 13b. That is EQU Y2=D.sup.2 .multidot..pi./4
Comparing both pressure receiving areas Y1, Y2, it is clear that the valve body 13 of the cap 11 has larger pressure receiving area and therefore the cap 11 type can easily obtain good valve characteristics at the positive pressure state.
Consequently, the cap 1 type using the valve 3 where the inner and outer circumferential lip elements 3a, 3b are projected in reverse directions to each other is advantageous in that the pressure receiving area of the inner circumferential lip element 3a is made larger, but is disadvantageous in that the pressure receiving area of the outer circumferential lip element 3b is made smaller.